The MUSIC/SP file system was unique in a number of respects. There was a single system-wide file index. The owner's userid and the file name were hashed to locate the file in this index, so any file on the system could be located with a single I/O operation. However, this presented a flat file system to the user. It lacked the directory structure commonly offered by DOS, Windows and Unix systems. In 1990 a "tree-structured" directory view of the file system was overlaid on this, bringing the system more in line with the file systems that were then available. By default the information stored in the files was compressed. This offered considerable saving in disk space. The file system had a fairly sophisticated access control scheme allowing the owner to control who could read, write, append to and execute the file. It also had the concept of a "public" file which was visible to all users and a "private" file which was only visible to the owner. In version 2.3, even private files were listed in the common library, with the result that no two users could have files under the same name; by 4.0, this limitation was removed.

Virtual memory

The initial versions of the system provided no support for virtual memory and address translation. Only one active user could reside in core memory at any time. Swapping (to disk) was used to time-share between different users, and a variable-length timeslice was used. Virtual memory support was introduced in 1985. This allowed multiple users to be in core memory at the same time, removed many of the restrictions in the size of the programs that could be run and provided a significant performance improvement. System performance was also improved by pre-loading commonly used modules into virtual memory at startup time where they could be available to all users simultaneously.

Programming languages

The system was designed to support academic computing and the teaching of computer science, so a rich suite of programming languages was available. The system nucleus was written in IBM/370 assembler but most of the native applications were written in FORTRAN. The system supported the Waterloo WATFIV and WATBOL compilers and also provided compilers for Pascal, C, PL/I, BASIC, APL, ALGOL, RPG, and GPSS. The system was missing a command scripting language until REXX was ported from CMS in 1984. Later, in 1986, a complete user interface was written entirely in REXX.

E-mail and the Internet

E-mail was one of the major applications on MUSIC/SP. The e-mail interface initially provided access to local e-mail. As the networks developed, this was expanded to provide access to BITNET and Internet based e-mail. MUSIC/SP did not have direct access to the Internet until 1990, when the University of Wisconsin WiscnetTCP/IP code was ported to the system, allowing the system to provide access to all Internet services.

Compatibility with other IBM systems

A major feature of the system was its ability to run programs that were designed to run on IBM's mainstream operating system (MVS). This was accomplished using an MVS emulator that intercepted system calls at the Supervisor Call instruction (SVC) level. Most third-party applications ran in this mode. Rather than write their own version of an application, the MUSIC/SP developers would usually start from the MVS version and rebuild it to run in MVS emulation mode. Since the MVS emulation was a very limited subset of the real thing, the applications generally ran more efficiently on MUSIC/SP.

Other features

One major advantage the system had in educational environments was that through the use of special lines called "control cards" at the top of a file, source files for any supported language could be automatically directed to the appropriate compiler (Fortran being the default), compiled, linked, and executed, (with compilation, linkage, and execution options also specified in control cards) simply by entering the filename on a command line.

A wide variety of terminals were supported as of 1980, including both EBCDIC-based units using IBM-proprietary protocols, and asynchronous ASCII-based units. Since terminals were connected through various types of front-end processors (as per common IBM timesharing practice both then and now), and could therefore function without CPU attention for a considerable amount of time, MUSIC used variable-length time slices, which could, on compute-bound processing, reach a maximum of several seconds per time slice; conversely, if a user filled the output buffer or reached a conversational read, the timeslice would end immediately.

The Sim390 emulator that runs on Microsoft Windows contains a demonstration system of MUSIC/SP. It is freely available. The demonstration system will also run under Hercules, for those users who do not run Windows.

1.
McGill University
–
McGill University is a public research university in Montreal, Quebec, Canada. It was established in 1821 by royal charter, issued by King George IV of Great Britain, the University bears the name of James McGill, a prominent Montreal merchant from Scotland whose bequest in 1813 formed the universitys precursor, McGill College. Its academic units are organized into 11 main Faculties and Schools, McGill offers degrees and diplomas in over 300 fields of study, with the highest average admission requirements of any Canadian university. Most students are enrolled in the five largest faculties, namely Arts, Science, Medicine, Engineering, tuition fees vary significantly between in-province, out-of-province, and international students, as well as between faculties. Scholarships are generous, yet highly competitive and relatively difficult to attain, throughout its long history, McGill alumni were instrumental in inventing or initially organizing football, basketball, and ice hockey. In 1816 the RIAL was authorized to operate two new Royal Grammar Schools, in Quebec City and in Montreal and this was an important first step in the creation of nondenominational schools. When James McGill died in 1813 his bequest was administered by the RIAL, the original two Royal Grammar Schools closed in 1846 and by the mid-19th century the RIAL lost control of the other 82 grammar schools it had administered. Its sole remaining purpose was to administer the McGill bequest on behalf of the private college, since the revised Royal Charter of 1852, The Trustees of the RIAL comprise the Board of Governors of McGill University. James McGill, born in Glasgow, Scotland on 6 October 1744, was a merchant in Quebec. Between 1811 and 1813, he drew up a will leaving his Burnside estate, a 19-hectare tract of rural land and 10,000 pounds to the Royal Institution for the Advancement of Learning. As a condition of the bequest, the land and funds had to be used for the establishment of a University or College, for the purposes of Education and the Advancement of Learning in the said Province. On March 31,1821, after protracted battles with the Desrivières family. The Charter provided that the College should be deemed and taken as a University, the Faculty of Medicine granted its first degree, a Doctor of Medicine and Surgery, in 1833, this was also the first medical degree to be awarded in Canada. The Faculty of Medicine remained the only functioning faculty until 1843 when the Faculty of Arts commenced teaching in the newly constructed Arts Building. The university also historically has strong linkage with The Canadian Grenadier Guards and this title is marked upon the stone that stands before the Arts building, from where the Guards step off annually to commemorate Remembrance Day. The Faculty of Law was founded in 1848 which is also the oldest of its kind in the nation,48 years later, the school of architecture at McGill University was founded. Sir John William Dawson, McGills principal from 1855 to 1893, is credited with transforming the school into a modern university. He recruited the aid of Montreals wealthiest citizens, many of whom donated property and their names adorn many of the campuss prominent buildings

2.
IBM System/360
–
The IBM System/360 is a mainframe computer system family that was announced by IBM on April 7,1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover the range of applications, from small to large. The design made a distinction between architecture and implementation, allowing IBM to release a suite of compatible designs at different prices. The launch of the System/360 family introduced IBMs Solid Logic Technology, the slowest System/360 model announced in 1964, the Model 30, could perform up to 34,500 instructions per second, with memory from 8 to 64 KB. The 1967 IBM System/360 Model 91 could do up to 16.6 million instructions per second, up to 8 megabytes of slower Large Capacity Storage was also available. Many consider the one of the most successful computers in history. The chief architect of System/360 was Gene Amdahl, and the project was managed by Fred Brooks, the commercial release was piloted by another of Watsons lieutenants, John R. Opel, who managed the launch of IBM’s System 360 mainframe family in 1964. Application level compatibility for System/360 software is maintained to present day with the System z servers, contrasting with at-the-time normal industry practice, IBM created an entire series of computers, from small to large, low to high performance, all using the same instruction set. This feat allowed customers to use a model and then upgrade to larger systems as their needs increased without the time. This flexibility greatly lowered barriers to entry, with other vendors, customers had to choose between machines they could outgrow and machines that were potentially overpowered. This meant that many simply did not buy computers. IBM initially announced a series of six computers and forty common peripherals, IBM eventually delivered fourteen models, including rare one-off models for NASA. The initial announcement in 1964 included Models 30,40,50,60,62, the first three were low- to middle-range systems aimed at the IBM1400 series market. All three first shipped in mid-1965, the last three, intended to replace the 7000 series machines, never shipped and were replaced by the 65 and 75, which were first delivered in November 1965, and January 1966, respectively. Later additions to the low-end included models 20,22, and 25, the Model 20 had several sub-models, sub-model 5 was at the higher end of the model. A succession of high-end machines included the Model 67,85,91,95, the 85 design was intermediate between the System/360 line and the follow-on System/370 and was the basis for the 370/165. There was a System/370 version of the 195, but it did not include Dynamic Address Translation, the implementations differed substantially, using different native data path widths, presence or absence of microcode, yet were extremely compatible. Except where specifically documented, the models were architecturally compatible, the 91, for example, was designed for scientific computing and provided out-of-order instruction execution, but lacked the decimal instruction set used in commercial applications

3.
IBM mainframe
–
IBM mainframes are large computer systems produced by IBM since 1952. During the 1960s and 1970s, the mainframe computer was almost synonymous with IBM products due to their marketshare. Current mainframes in IBMs line of computers are developments of the basic design of the IBM System/360. From 1952 into the late 1960s, IBM manufactured and marketed several large computer models, the first-generation 700s were based on vacuum tubes, while the later, second-generation 7000s used transistors. These machines established IBMs dominance in electronic data processing, IBM had two model categories, one for engineering and scientific use, and one for commercial or data processing use. The two categories, scientific and commercial, generally used common peripherals but had completely different instruction sets, IBM initially sold its computers without any software, expecting customers to write their own, programs were manually initiated, one at a time. Later, IBM provided compilers for the newly developed higher-level programming languages Fortran, the first operating systems for IBM computers were written by IBM customers who did not wish to have their very expensive machines sitting idle while operators set up jobs manually. These first operating systems were essentially scheduled work queues and it is generally thought that the first operating system used for real work was GM-NAA I/O, produced by General Motors Research division in 1956. IBM enhanced one of GM-NAA I/Os successors, the SHARE Operating System, the second generation products were a mainstay of IBMs business and IBM continued to make them for several years after the introduction of the System/360. Prior to System/360, IBM also sold computers smaller in scale that were not considered mainframes, though they were still bulky, the 7010 was introduced in 1962 as a mainframe-sized 1410. The later Systems 360 and 370 could emulate the 1400 machines, a desk size machine with a different instruction set, the IBM1130, was released concurrently with the System/360 to address the niche occupied by the 1620. It used the same EBCDIC character encoding as the 360 and was programmed in Fortran. Midrange computer is a used by IBM for a class of computer systems which fall in between mainframes and microcomputers. All that changed with the announcement of the System/360 in April,1964, the System/360 was a single series of compatible models for both commercial and scientific use. The number 360 suggested a 360 degree, or all-around computer system, System/360 incorporated features which had previously been present on only either the commercial line or the engineering and scientific line. Some of the units and addressing features were optional on some models of the System/360. However, models were compatible and most were also downward compatible. The System/360 was also the first computer in use to include dedicated hardware provisions for the use of operating systems

4.
Michigan Terminal System
–
The Michigan Terminal System is one of the first time-sharing computer operating systems. Among them is a subsystem, called MTS, for command interpretation, execution control, file management. End-users interact with the computers resources through MTS using terminal, batch, and server oriented facilities. MTS was used on a basis at 12 or 13 sites in the United States, Canada, the United Kingdom, Brazil. MTS was developed and maintained by a group of eight universities included in the MTS Consortium. The University of Michigan announced in 1988 that Reliable MTS service will be provided as long as there are users requiring it, MTS may be phased out after alternatives are able to meet users computing requirements. It ceased operating MTS for end-users on June 30,1996, by that time, most services had moved to client/server-based computing systems, typically Unix for servers and various Mac, PC, and Unix flavors for clients. The University of Michigan shut down its MTS system for the last time on May 30,1997, rensselaer Polytechnic Institute is believed to be the last site to use MTS in a production environment. RPI retired MTS in June 1999, today MTS still runs using IBM S/370 emulators such as Hercules, Sim390, and FLEX-ES. At that time the work that computers could perform was limited by their lack of memory storage capacity. The paper outlined a virtual memory architecture using dynamic address translation that could be used to implement time-sharing, the computer was dubbed the Model S/360-65M. But IBM initially decided not to supply a time-sharing operating system for the machine and they were all intrigued by the time-sharing idea and expressed interest in ordering the modified IBM S/360 series machines. With this demonstrated interest IBM changed the model number to S/360-67. Development of TSS took longer than anticipated, its date was delayed. At this time UM had to decide whether to return the Model 67, the decision was to continue development of MTS and the staff moved their initial development work from the Model 50 to the Model 67. TSS development was canceled by IBM, then reinstated. But by this time UM liked the system they had developed, it was no longer considered interim, many MTS components are the work of multiple people at multiple sites. Later, e-mail, computer conferencing using CONFER and *Forum, network file transfer, the members of the MTS Consortium produced a series of 82 MTS Newsletters between 1971 and 1982 to help coordinate MTS development

5.
Unix
–
Among these is Apples macOS, which is the Unix version with the largest installed base as of 2014. Many Unix-like operating systems have arisen over the years, of which Linux is the most popular, Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmer users. The system grew larger as the system started spreading in academic circles, as users added their own tools to the system. Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration and these concepts are collectively known as the Unix philosophy. By the early 1980s users began seeing Unix as a universal operating system. Under Unix, the system consists of many utilities along with the master control program. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space, the microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a disk for storage and a data terminal for input and output. However, modern systems include networking and other new devices, as graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse. In the 1980s, non-blocking I/O and the set of inter-process communication mechanisms were augmented with Unix domain sockets, shared memory, message queues, and semaphores. In microkernel implementations, functions such as network protocols could be moved out of the kernel, Multics introduced many innovations, but had many problems. Frustrated by the size and complexity of Multics but not by the aims and their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale. The name Unics, a pun on Multics, was suggested for the project in 1970. Peter H. Salus credits Peter Neumann with the pun, while Brian Kernighan claims the coining for himself, in 1972, Unix was rewritten in the C programming language. Bell Labs produced several versions of Unix that are referred to as Research Unix. In 1975, the first source license for UNIX was sold to faculty at the University of Illinois Department of Computer Science, UIUC graduate student Greg Chesson was instrumental in negotiating the terms of this license. During the late 1970s and early 1980s, the influence of Unix in academic circles led to adoption of Unix by commercial startups, including Sequent, HP-UX, Solaris, AIX. In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4, in the 1990s, Unix-like systems grew in popularity as Linux and BSD distributions were developed through collaboration by a worldwide network of programmers

6.
IBM AIX
–
AIX is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms. AIX is based on UNIX System V with 4. 3BSD-compatible extensions and it is one of five commercial operating systems that have versions certified to The Open Groups UNIX03 standard. The AIX family of operating systems debuted in 1986, became the operating system for the RS/6000 series on its launch in 1990. It is currently supported on IBM Power Systems alongside IBM i, Unix started life at AT&Ts Bell Labs research center in the early 1970s, running on DEC minicomputers. By 1976, the system was in use at various academic institutions, including Princeton. This port would later grow out to become UTS, a mainframe Unix offering by IBMs competitor Amdahl Corporation, IBMs own involvement in Unix can be dated to 1979, when it assisted Bell Labs in doing its own Unix port to the 370. In the process, IBM made modifications to the TSS/370 hypervisor to better support Unix and it took until 1985 for IBM to offer its own Unix on the S/370 platform, IX/370, which was developed by Interactive Systems Corporation and intended by IBM to compete with Amdahl UTS. AIX Version 1, introduced in 1986 for the IBM6150 RT workstation, was based on UNIX System V Releases 1 and 2, in developing AIX, IBM and Interactive Systems Corporation also incorporated source code from 4.2 and 4.3 BSD UNIX. Among other variants, IBM later produced AIX Version 3, based on System V Release 3, since 1990, AIX has served as the primary operating system for the RS/6000 series. AIX Version 4, introduced in 1994, added symmetric multiprocessing with the introduction of the first RS/6000 SMP servers and continued to evolve through the 1990s, culminating with AIX4.3.3 in 1999. Version 4.1, in a modified form, was also the standard operating system for the Apple Network Server systems sold by Apple Computer to complement the Macintosh line. IBM maintains that their license was irrevocable, and continued to sell, AIX was a component of the 2003 SCO v. IBM lawsuit, in which the SCO Group filed a lawsuit against IBM, alleging IBM contributed SCOs intellectual property to the Linux codebase. The SCO Group, who argued they were the owners of the copyrights covering the Unix operating system. In March 2010, a jury returned a finding that Novell, not the SCO Group. AIX6 was announced in May 2007, and it ran as an open beta from June 2007 until the availability of AIX6.1 on November 9,2007. Major new features in AIX6.1 included full role-based access control, workload partitions, enhanced security, AIX7.1 was announced in April 2010, and an open beta ran until general availability of AIX7.1 in September 2010. Several new features, including better scalability, enhanced clustering and management capabilities were added, AIX7.1 includes a new built-in clustering capability called Cluster Aware AIX. AIX is able to organize multiple LPARs through the communications channel to neighboring CPUs

7.
Computer terminal
–
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system. The function of a terminal is confined to display and input of data, a terminal that depends on the host computer for its processing power is called a dumb terminal or thin client. A personal computer can run terminal emulator software that replicates the function of a terminal, sometimes allowing concurrent use of local programs and access to a distant terminal host system. The terminal of the first working programmable, fully automatic digital Turing-complete computer, the Z3, had a keyboard, early user terminals connected to computers were electromechanical teleprinters/teletypewriters, such as the Teletype Model 33 ASR, originally used for telegraphy or the Friden Flexowriter. Later printing terminals such as the DECwriter LA30 were developed, however printing terminals were limited by the speed at which paper could be printed, and for interactive use the paper record was unnecessary. The problem was that the amount of memory needed to store the information on a page of text was comparable to the memory in low end minicomputers then in use. Displaying the information at video speeds was also a challenge and the control logic took up a rack worth of pre-integrated circuit electronics. Another approach involved the use of the tube, a specialized CRT developed by Tektronix that retained information written on it without the need to refresh. The Datapoint 3300 from Computer Terminal Corporation was announced in 1967 and shipped in 1969 and it solved the memory space issue mentioned above by using a digital shift-register design, and using only 72 columns rather than the later more common choice of 80. Some type of blinking cursor that can be positioned, the term intelligent in this context dates from 1969. Notable examples include the IBM2250 and IBM2260, predecessors to the IBM3270, providing even more processing possibilities, workstations like the Televideo TS-800 could run CP/M-86, blurring the distinction between terminal and Personal Computer. Most terminals were connected to minicomputers or mainframe computers and often had a green or amber screen, typically terminals communicate with the computer via a serial port via a null modem cable, often using an EIA RS-232 or RS-422 or RS-423 or a current loop serial interface. In fact, the design for the Intel 8008 was originally conceived at Computer Terminal Corporation as the processor for the Datapoint 2200. While early IBM PCs had single color green screens, these screens were not terminals. The screen of a PC did not contain any character generation hardware, all signals and video formatting were generated by the video display card in the PC, or by the CPU. An IBM PC monitor, whether it was the monochrome display or the 16-color display, was technically much more similar to an analog TV set than to a terminal. With suitable software a PC could, however, emulate a terminal, the Data General One could be booted into terminal emulator mode from its ROM. Since the advent and subsequent popularization of the computer, few genuine hardware terminals are used to interface with computers today

8.
IBM
–
International Business Machines Corporation is an American multinational technology company headquartered in Armonk, New York, United States, with operations in over 170 countries. The company originated in 1911 as the Computing-Tabulating-Recording Company and was renamed International Business Machines in 1924, IBM manufactures and markets computer hardware, middleware and software, and offers hosting and consulting services in areas ranging from mainframe computers to nanotechnology. IBM is also a research organization, holding the record for most patents generated by a business for 24 consecutive years. IBM has continually shifted its business mix by exiting commoditizing markets and focusing on higher-value, also in 2014, IBM announced that it would go fabless, continuing to design semiconductors, but offloading manufacturing to GlobalFoundries. Nicknamed Big Blue, IBM is one of 30 companies included in the Dow Jones Industrial Average and one of the worlds largest employers, with nearly 380,000 employees. Known as IBMers, IBM employees have been awarded five Nobel Prizes, six Turing Awards, ten National Medals of Technology, in the 1880s, technologies emerged that would ultimately form the core of what would become International Business Machines. On June 16,1911, their four companies were amalgamated in New York State by Charles Ranlett Flint forming a fifth company, the Computing-Tabulating-Recording Company based in Endicott, New York. The five companies had 1,300 employees and offices and plants in Endicott and Binghamton, New York, Dayton, Ohio, Detroit, Michigan, Washington, D. C. and Toronto. They manufactured machinery for sale and lease, ranging from commercial scales and industrial time recorders, meat and cheese slicers, to tabulators and punched cards. Thomas J. Watson, Sr. fired from the National Cash Register Company by John Henry Patterson, called on Flint and, Watson joined CTR as General Manager then,11 months later, was made President when court cases relating to his time at NCR were resolved. Having learned Pattersons pioneering business practices, Watson proceeded to put the stamp of NCR onto CTRs companies and his favorite slogan, THINK, became a mantra for each companys employees. During Watsons first four years, revenues more than doubled to $9 million, Watson had never liked the clumsy hyphenated title of the CTR and in 1924 chose to replace it with the more expansive title International Business Machines. By 1933 most of the subsidiaries had been merged into one company, in 1937, IBMs tabulating equipment enabled organizations to process unprecedented amounts of data, its clients including the U. S. During the Second World War the company produced small arms for the American war effort, in 1949, Thomas Watson, Sr. created IBM World Trade Corporation, a subsidiary of IBM focused on foreign operations. In 1952, he stepped down after almost 40 years at the company helm, in 1957, the FORTRAN scientific programming language was developed. In 1961, IBM developed the SABRE reservation system for American Airlines, in 1963, IBM employees and computers helped NASA track the orbital flight of the Mercury astronauts. A year later it moved its headquarters from New York City to Armonk. The latter half of the 1960s saw IBM continue its support of space exploration, on April 7,1964, IBM announced the first computer system family, the IBM System/360

9.
Data compression
–
In signal processing, data compression, source coding, or bit-rate reduction involves encoding information using fewer bits than the original representation. Compression can be lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy, no information is lost in lossless compression. Lossy compression reduces bits by removing unnecessary or less important information, the process of reducing the size of a data file is referred to as data compression. In the context of data transmission, it is called coding in opposition to channel coding. Compression is useful because it reduces resources required to store and transmit data, computational resources are consumed in the compression process and, usually, in the reversal of the process. Data compression is subject to a space–time complexity trade-off, Lossless data compression algorithms usually exploit statistical redundancy to represent data without losing any information, so that the process is reversible. Lossless compression is possible because most real-world data exhibits statistical redundancy, for example, an image may have areas of color that do not change over several pixels, instead of coding red pixel, red pixel. The data may be encoded as 279 red pixels and this is a basic example of run-length encoding, there are many schemes to reduce file size by eliminating redundancy. The Lempel–Ziv compression methods are among the most popular algorithms for lossless storage, DEFLATE is a variation on LZ optimized for decompression speed and compression ratio, but compression can be slow. DEFLATE is used in PKZIP, Gzip, and PNG, LZW is used in GIF images. LZ methods use a table-based compression model where table entries are substituted for repeated strings of data, for most LZ methods, this table is generated dynamically from earlier data in the input. The table itself is often Huffman encoded, current LZ-based coding schemes that perform well are Brotli and LZX. LZX is used in Microsofts CAB format, the best modern lossless compressors use probabilistic models, such as prediction by partial matching. The Burrows–Wheeler transform can also be viewed as a form of statistical modelling. The basic task of grammar-based codes is constructing a context-free grammar deriving a single string, sequitur and Re-Pair are practical grammar compression algorithms for which software is publicly available. In a further refinement of the use of probabilistic modelling. Arithmetic coding is a more modern coding technique that uses the mathematical calculations of a machine to produce a string of encoded bits from a series of input data symbols

10.
DOS/360 and successors
–
Disk Operating System/360, also DOS/360, or simply DOS, is a discontinued operating system for IBM mainframes. It was announced by IBM on the last day of 1964, in its time, DOS/360 was the most widely used operating system in the world. TOS/360 was an IBM operating system for the System/360, used in the days around 1965 to support the IBM360 model 30. TOS, as per the Tape in the name, required a tape drive and it shared most of the code base and some manuals with IBMs DOS/360. DOS/360 was the operating system for most small to midsize S/360 installations. The first DOS/VS release was numbered Release 28 to signify an incremental upgrade from DOS/360 and it added virtual memory in support of the new System/370 series hardware. It used a fixed page table which mapped a single space of up to 16 megabytes for all partitions combined. DOS/VS increased the number of partitions from three to five and allowed a system total of fifteen subtasks. DOS/VS was succeeded by DOS/VSE through z/VSE, DOS/VSE was introduced in 1979 as an extended version of DOS/VS to support the new 4300 processors. The 4300 systems included a feature called ECPS, VSE that provided a storage for both the processor and the I/O channels. DOS/VSE provided support for ECPS, VSE, but could run on a System/370 without that feature. VSE was the last free version of DOS, SSX/VSE was an attempt by IBM to simplify purchase and installation of VSE by providing a pre-generated system containing the OS and the most popular products. SSX was released in 1982, and later replaced by VSE/SP, in 1986 IBM released VSE/SP in conjunction with the announcement of the 9370 processors. VSE/SP replaced SSX/VSE and bundled VSE with the most popular VSE program products such as VSE/AF, ACF/VTAM, CICS, VSE/SP supported only 24-bit addresses, despite customer requests to provide an XA version. VSE/ESA was a 31-bit DOS/VSE version, which was released in 1990 with support for up to 384 MB of real storage and it provided up to twelve static partitions and allowed VSE/POWER and ACF/VTAM to be run in private address spaces. It introduced a new feature called dynamic partitions which could allow up to 150 concurrent jobs, version 1 could run in either ESA or 370 mode, with the ESA mode also supporting XA hardware with limitations. Version 2 only supported ESA mode with ESA hardware, IBM released z/VSE3.1 in 2005. This change in naming reflected the new System z branding for IBMs mainframe product line, in particular, it did not support the new 64-bit z/Architecture, running only in 31-bit mode even on 64-bit capable machines

11.
Z/OS
–
Z/OS is a 64-bit operating system for IBM mainframes, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions, like OS/390, z/OS combines a number of formerly separate, related products, some of which are still optional. Z/OS offers the attributes of modern operating systems but also much of the functionality originating in the 1960s. Z/OS was first introduced in October 2000, as a result, z/OS hosts a broad range of commercial and open source software. Z/OS can communicate directly via TCP/IP, including IPv6, and includes standard HTTP servers along with common services such as FTP, NFS. Another central design philosophy is support for high quality of service, even within a single operating system instance. This capability inherently supports multi-tenancy within an operating system image. However, modern IBM mainframes also offer two levels of virtualization, LPARs and z/VM. These new functions within the hardware, z/OS, and z/VM — and Linux, many of them utilize the WebSphere Application Server for z/OS middleware. From its inception z/OS has supported tri-modal addressing, IBM support for z/OS1.5 ended on March 31,2007. Now z/OS is only supported on z/Architecture mainframes and only runs in 64-bit mode, z/Architecture hardware always starts running in 31-bit mode, but current z/OS releases quickly switch to 64-bit mode and will not run on hardware that does not support 64-bit mode. However, increasing numbers of products and applications, such as DB2 Version 8 and above, now require. IBM markets z/OS as its operating system, suited for continuous. U. S. standard commercial z/OS pricing starts at about $125 per month, including support, z/OS introduced Variable Workload License Charges and Entry Workload License Charges which are sub-capacity billing options. VWLC and EWLC customers only pay for peak monthly z/OS usage, VWLC and EWLC are also available for most IBM software products running on z/OS, and their peaks are separately calculated but can never exceed the z/OS peak. To be eligible for sub-capacity licensing, a customer must be running in 64-bit mode, must have completely eliminated OS/390 from the system. Sub-capacity billing substantially reduces software charges for most IBM mainframe customers, advanced Workload License Charges is the successor to VWLC on mainframe models starting with the zEnterprise 196, and EAWLC is an option on zEnterprise 114 models. AWLC and EAWLC offer further sub-capacity discounts, within each address space, z/OS typically permits the placement of only data, not code, above the 2 GB bar

Comparison of spectrograms of audio in an uncompressed format and several lossy formats. The lossy spectrograms show bandlimiting of higher frequencies, a common technique associated with lossy audio compression.